How Antibiotic Resistance Happens

Antibiotics inhibit the growth of bacteria that make humans and animals sick. An antibiotic works by penetrating a bacterial cell wall. It looks for a target with specific enzymes involved in daily functions of the cell, and disrupts them so the bacteria can’t replicate.

Heather Kittrell is a postdoc research assistant with the Swine Medicine Education Center at Iowa State University. She says some bacteria are naturally resistant.

"That bacteria doesn’t have the target that that antibiotic needs to bind to, and therefore it doesn’t work. Example of this, mycoplasma is resistant to penicillin. There’s nothing that we could do to change this," says Kittrell. "Knowledge of this intrinsic resistance of the pathogen is important in avoiding inappropriate or ineffective therapies that can lead to acquired resistance."

With “acquired resistance,” the bacteria cell has the target and has responded to the antibiotic at some point, but the bacteria has made changes so it’s no longer affected by the drug.

"The bacteria can produce enzymes that inactivate the drug by destroying or adding chemical compounds that do not allow interaction," she says. "They can also modify target sites so that the antibiotic has less of an attraction to the site that it normally binds to."

Bacteria will inevitably find ways around the drugs we humans develop to stop them. This is why judicial use of antibiotics is critical to slow that process down.

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